1. Field of the Invention
The present invention relates to a shank for a rotary and/or percussive tool such as trepan, chisel, or annular bit with a diameter up to 150 mm for working stone, concrete, or brickwork, and a chuck for receiving the shank.
2. Description of the Prior Art
Generally, a rotary and percussive tool has a shank with round guide regions, axially closed locking grooves, and entrain grooves open at their power tool side, with radially displaceable locking elements of a chuck, in which the shank is received, engaging in the locking grooves and limiting the axial displacement of the working tool. The radially inwardly located, with respect to the outer surfaces of the guide region, entrain surfaces require, because of their small radial depth, high surface pressures for transmitting a torque. This leads to an early or premature wear of these surfaces. Furthermore, because such grooves are formed by machining in a round shank, the cross-sectional surface available for transmission of impacts to the working tool is reduced.
U.S. Pat. No. 2,047,125 discloses a shank for a rotary and percussive tool and which has a plurality of axially offset, radially projecting entrain surfaces having a rectangular or trapezoidal cross-section.
U.S. Pat. No. 5,984,596 discloses a shank for a rotary and percussive tool having a locking groove for receiving a locking member radially engaging therein, and two diametrically opposite, radially projecting, rhomboidal entrain surfaces. In the discloses shank, there is a sharp transition from the round guide regions to the entrain surfaces. This leads, at an impact load, to reflection of a generated load pulse and, thus, to a reduced drilling capacity of the tool. In addition, the manufacture of such shanks is time-consuming and expensive.
French Patent No. 2,408,716 discloses a shank with radially projecting entrain strips which for limiting axial displacement, have their axial end surfaces being contacted by locking elements of a chuck. The entrain strips are obtained by deforming the shank with round guide regions. With locking being effected by contact with the radially outer end surfaces of the entrain strips, a relatively large radial depth of the chuck, with respect to the diameter of the shank, is required. The pressed-in grooves with an acute angle and small axial stop surfaces are not suitable for properly engaging the locking elements.
Accordingly, an object of the present invention is to provide a shank for a rotary and percussive tool capable of transmitting a high torque without any noticeable wear from a chuck having a relatively small radial depth, and having good pulse behavior.
A further object of the invention is to provide a shank of a type described above that can be formed with using less material and in a shorter time than a conventional chuck.